[PATCH v1 5/7] iio: adc: ina2xx: Use a monotonic clock for delay calculation

[Stefan Brüns]

The iio timestamp clock is user selectable and may be non-monotonic. Also,
only part of the acquisition time is measured, thus the delay was longer
than intended.

Signed-off-by: Stefan Brüns <stefan.bru...@rwth-aachen.de>
---

 drivers/iio/adc/ina2xx-adc.c | 35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c
index 2621a34ee5c6..65bd9e69faf2 100644
--- a/drivers/iio/adc/ina2xx-adc.c
+++ b/drivers/iio/adc/ina2xx-adc.c
@@ -703,10 +703,10 @@ static int ina2xx_work_buffer(struct iio_dev *indio_dev)
        /* data buffer needs space for channel data and timestap */
        unsigned short data[4 + sizeof(s64)/sizeof(short)];
        int bit, ret, i = 0;
-       s64 time_a, time_b;
+       s64 time;
        unsigned int alert;
 
-       time_a = iio_get_time_ns(indio_dev);
+       time = iio_get_time_ns(indio_dev);
 
        /*
         * Because the timer thread and the chip conversion clock
@@ -752,11 +752,9 @@ static int ina2xx_work_buffer(struct iio_dev *indio_dev)
                data[i++] = val;
        }
 
-       time_b = iio_get_time_ns(indio_dev);
+       iio_push_to_buffers_with_timestamp(indio_dev, data, time);
 
-       iio_push_to_buffers_with_timestamp(indio_dev, data, time_a);
-
-       return (unsigned long)(time_b - time_a) / 1000;
+       return 0;
 };
 
 static int ina2xx_capture_thread(void *data)
@@ -764,7 +762,9 @@ static int ina2xx_capture_thread(void *data)
        struct iio_dev *indio_dev = data;
        struct ina2xx_chip_info *chip = iio_priv(indio_dev);
        int sampling_us = SAMPLING_PERIOD(chip);
-       int buffer_us, delay_us;
+       int ret;
+       struct timespec64 next, now, delta;
+       s64 delay_us;
 
        /*
         * Poll a bit faster than the chip internal Fs, in case
@@ -773,15 +773,22 @@ static int ina2xx_capture_thread(void *data)
        if (!chip->allow_async_readout)
                sampling_us -= 200;
 
+       ktime_get_ts64(&next);
+
        do {
-               buffer_us = ina2xx_work_buffer(indio_dev);
-               if (buffer_us < 0)
-                       return buffer_us;
+               ret = ina2xx_work_buffer(indio_dev);
+               if (ret < 0)
+                       return ret;
 
-               if (sampling_us > buffer_us) {
-                       delay_us = sampling_us - buffer_us;
-                       usleep_range(delay_us, (delay_us * 3) >> 1);
-               }
+               ktime_get_ts64(&now);
+
+               do {
+                       timespec64_add_ns(&next, 1000 * sampling_us);
+                       delta = timespec64_sub(next, now);
+                       delay_us = timespec64_to_ns(&delta) / 1000;
+               } while (delay_us <= 0);
+
+               usleep_range(delay_us, (delay_us * 3) >> 1);
 
        } while (!kthread_should_stop());
 
-- 
2.15.1